1. Field of the Invention
This invention relates to fluid-film bearings for rotating machinery and more particularly to thrust bearings which include unique resilient load-supporting bearing-insert assemblies.
2. Description of the Prior Art
Hydrodynamic thrust bearings are well known in the art and have been used effectively as supports for rotating machinery, including high-speed applications. The term hydrodynamic thrust bearing, as used herein, is meant to describe that class of fluid-film thrust bearings which has its surfaces separated by a thin layer of either liquid or gas, the film being established and the pressure generated therein by the relative motion between the bearing surfaces. This, of course, is distinct from bearings of the hydrostatic type, which require feed of pressurized fluid from an external source.
In the main, past hydrodynamic thrust bearings have usually been rigid and rigidly mounted and thus not self-aligning, unless provided with complex, expensive and frequently troublesome gimbal and pivot supports. Typical examples are the tapered-land, the Rayleigh step and pocket bearings, and the non-radially grooved (e.g., spiral or herringbone) pumping plates, the latter having particularly efficient load-generating ability. For further discussion, see D. D. Fuller, "A Review of the State-of-the-Art for the Design of Self-Acting Gas-Lubricated Bearings," Journal of Lubrication Technology, Trans. ASME, Vol. 91, Ser. F, No. 1, Janary 1969, pp. 1-16. These bearings have been prone to damage and destruction caused by excursions and contact by the runner due to unavoidable misalignment, whether due to manufacture and assembly, thermal distortion, or nutation (wobble) of the runner caused by unbalance. This is particularly true when excursions are large, as in the resonant speed-range. Although gimbals may be used for mounting stator plates to provide static alignment, they are relatively massive and prevent effective tracking of the runner at medium and high speeds. Furthermore, the increased degrees of freedom provided by gimbals introduce additional and dangerous resonances. Moreover, gimbal systems are frequently the cause of instability and ensuing destruction of both rotor and bearings. Similar deficiencies apply to bearings of the pivoted-shoe type which, although self-aligning, are generally complex, expensive, prone to pivot fretting and surface damage, and subject to dynamic problems, especially if gas-lubricated and operated at high speed. Overall, it is recognized that prior-art rigid and rigidly mounted, hydrodynamic thrust bearings have been frequently subject to destruction and degradation due to dynamic problems and surface deterioration, and that their operation at small clearances and high speeds has been particularly dangerous, with contact between surfaces of the thrust bearing and entry of particles posing the risk of severe damage or destruction.
Recent efforts to improve hydrodynamic bearings have resulted in compliant hydrodynamic thrust bearings equipped with foil-insert assemblies designed to generate lubricating films and to support loads. Some, such as those shown in U.S. Pat. Nos. 3,375,046; 3,382,014 and 3,635,534, may employ a plurality of bearing foils and some, such as those shown in U.S. Pat. Nos. 3,747,997 and 3,809,443, may use a unitary bearing foil. All, however, rely on the relatively uncontrolled formation of a lubricating wedge, the shape of the lubricating wedge being critical in efficient generation of load capacity. Unfortunately, in prior and current art, this shape is more a matter of chance than of design.
In sum, although the prior art techniques may be useful, the need for further improvements has remained. Unquestionably, there is a need for a fluid-film thrust bearing for the support of high speed rotors (such as turbocompressors, turbochargers, turbogenerators, turbine gas generators, cryogenic expanders, blowers, pumps, aircraft air-cycle machines, centrifuges, scanners, yarn spinners and processors and the like) which can accomplish all of the following:
1. follow both the wobble and axial motion of the runner in the entire operating range of the machine, and particularly at high speeds;
2. accommodate initial misalignment of assembly and also misalignment due to thermal distortion of rotating and stationary machine elements;
3. tolerate foreign particles in the bearing clearance through local surface-deflection;
4. provide superior wipe-wear characteristics not only at high speeds, but also when starting and stopping; and
5. compensate, at least partially, for thermal distortion (crowning).